Platypus genome decoded, according to reports in BBC News and ABC (Australia) News 7 May 2008 and Nature, vol. 453, p175, 8 May 2008. An international team of scientists has mapped the genome of the platypus and have revealed a “genetic potpourri” of mammal, bird and reptile genes, which fits with its unusual anatomy and function. The animal lays eggs like a reptile, and the young hatch out in a very immature state, and then live on milk. The genome study found genes for several milk proteins and one egg yolk protein.
Although the platypus does not have teeth it does have a gene for tooth enamel. The male platypus has a venom gland, and the venom is similar to reptile venom, but the platypus venom genes are different to those of reptiles. This is considered to be an example of convergent evolution.
The genetics of sex determination in the platypus is different from any other mammal. It has 10 sex chromosomes: 5 Xs and 5 Ys. Its X chromosome has some characteristics similar to the Z chromosome of birds, and the Y chromosome lacks a gene named SRY, an essential sex determining gene found in other mammals.
Scientists are using the platypus genome to construct the evolutionary tree of mammals and understand how they evolved from a common ancestor with reptiles. Richard Wilson, of Washington University commented: “By comparing the platypus genome to other mammalian genomes, we’ll be able to study genes that have been conserved throughout evolution.” Chris Ponting of Oxford University commented: “The platypus genome is extremely important, because it is the missing link in our understanding of how we and other mammals first evolved.” However, the curious mixture of genes is not making the job easy. Richard Gibbs, who directs the Human Genome Sequencing Center at Baylor College of Medicine in Houston Texas, commented. “There is nothing quite as enigmatic as a platypus. You have got these reptilian repeat patterns and these more recently evolved milk genes and independent evolution of the venom. It all points to how idiosyncratic evolution is.”
Editorial Comment: Rather than showing “idiosyncratic evolution” the platypus genome confirms that this animal is a unique combination of fully functioning features, well designed for the lifestyle and environment it lives in. Its unique sex chromosomes show that it is a separate kind, completely different from any mammal, bird or reptile. The fact that the living platypus has genes for tooth enamel, but not teeth, is interesting in light of the fact that fossil platypuses have teeth. It takes more than just the enamel gene to form teeth, so we conclude that in the time since fossil platypuses were buried, the animals have lost the ability to grow teeth (and have also shrunk in size). This is a degenerative process – not an evolution. The living and fossil facts about the platypus fit the Biblical history of creation followed by degeneration, not random evolution from an unknown ancestor. (Ref. monotremes, genomics, Ornithorhynchus)
Evidence News 21 May 2008